1. Field of the Invention
The present invention relates to a variable venturi-type carburetor with automatic vacuum regulation and cam control mechanism. More particularly, the present invention relates to a variable venturi-type carburetor capitalizing on changes of engine vacuum suction force and interaction of the cam to control the upward and downward displacement of a conical body in the variable venturi-type carburetor, thereby adjusting the air/fuel ratio in an appropriate range.
2. Description of the Related Art
Most present automobile carburetors are designed with a fixed venturi to create a vacuum pressure in the induction duct in order to pull fuel from a fuel reservoir. The venturi, by its fixed nature, operates at a maximum efficiency over a small range of engine RPM. Furthermore, a different size venturi is generally required for different size engines in performance requirements. To overcome the inefficiency of the prior art fixed venturi carburetor, various variable venturi carburetors have been developed. Compared to the traditional fixed venturi carburetors, variable venturi carburetors can effectively operate throughout the entire engine operation range.
FIG. 1 is a schematic, cross-sectional view illustrating a prior art variable venturi carburetor. As shown in FIG. 1, the prior art variable venturi carburetor includes a seat 6xe2x80x2, a main body 7xe2x80x2, an upper lid 8xe2x80x2, a variable venturi assembly 2xe2x80x2, a fuel reservoir 3xe2x80x2, and a path structure 4xe2x80x2. A central channel 10xe2x80x2 is defined by the seat 6xe2x80x2, the main body 7xe2x80x2 and the upper lid 8xe2x80x2. A throttle valve shaft 511xe2x80x2 is pivotally installed in the seat 6xe2x80x2. A switching rod 53xe2x80x2 is connected to the throttle valve shaft 511xe2x80x2. The main body 7xe2x80x2 comprises an upper flange 70xe2x80x2 approaching the upper lid 8xe2x80x2. A fixing ring 80xe2x80x2, which is fastened on the upper lid with screws, is situated at a position approaching the flange 70xe2x80x2 of the main body 7xe2x80x2 to define an outlet channel 40xe2x80x2. The variable venturi assembly 2xe2x80x2 comprises a support 20xe2x80x2, a shaft 211xe2x80x2, a conical body 21xe2x80x2, and a resilient member 22xe2x80x2. The support 20xe2x80x2 is fixed to the main body 7xe2x80x2. A pivot hole 213xe2x80x2 is provided in the support 20xe2x80x2. The lower end of the shaft 211xe2x80x2 is pivotally connected to the switching rod that is connected to the throttle valve shaft 511xe2x80x2. The conical body 21xe2x80x2 is connected and fixed to the upper end of the shaft 211xe2x80x2. The slightly curved surface of the conical body 21xe2x80x2 and the flange 70xe2x80x2 of the main body 7xe2x80x2 define a venturi throat-narrowing channel 13xe2x80x2. The resilient member 22xe2x80x2 is installed between the conical body 21xe2x80x2 and the support 20xe2x80x2 to push the conical body 21xe2x80x2 upwards. The path 4xe2x80x2 connects the fuel reservoir 3xe2x80x2 and the outlet channel 40xe2x80x2 to the venturi throat-narrowing channel 13xe2x80x2. By rotating the throttle valve shaft 511xe2x80x2, the shaft 211xe2x80x2 of the variable venturi assembly 2xe2x80x2 descends to change the size of the venturi throat narrowing path 13xe2x80x2, thereby obtaining a proper air/fuel ratio.
Since the above-described prior art variable venturi carburetor comprises the variable venturi assembly 2xe2x80x2 connected to the throttle valve shaft 511xe2x80x2, when braking, a sudden large vacuum suction force is created. When the vacuum suction force increases, the conical body of the variable venturi assembly is upwardly pushed by the resilient member, thereby narrowing the venturi throat channel. However, the above-described prior art variable venturi carburetor cannot control the precise position of the conical body when the sudden large vacuum suction force occurs to obtain an optimal spacing. This leads to an overly rich fuel-air mixture and thus results in air pollution. Furthermore, when the throttle valve is fully open, the spacing of the venturi throat channel is fixed. However, it is known that the power load on the engine varies with different road conditions (e.g. grade). Fixed spacing for a fully open throttle valve causes a waste of fuel when the vehicle moves on low-grade roads and inadequate power when vehicle moves on high-grade roads. Even for engines installed with a horse power regulation ring of vacuum valve controllable by engine vacuum suction force, the decrease of engine vacuum suction force caused by an over-loaded engine will make the vacuum valve lose its self-compensation ability.
Accordingly, the primary object of the present invention is to provide a variable venturi-type carburetor with automatic vacuum regulation and cam control mechanism for adjusting the air/fuel ratio over a wide operation range, thereby increasing the performance of engines.
To achieve this and other advantages and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a variable venturi-type carburetor with automatic vacuum regulation and cam control mechanism. The carburetor according to the invention comprises a base defining a central channel having an upper inlet end and a lower outlet end. A variable venturi assembly is situated in the middle of the central channel, the variable venturi assembly comprising a support, a conical body, and a resilient member. The support is fixed in the base, the bottom of the conical body is movably connected to the support and the surface of the conical body and the base define a venturi throat. The resilient member is situated between the support and the conical body. A fuel reservoir is provided in the base. A path structure connects the fuel reservoir and the venturi throat. A cam control mechanism comprises a cam set, throttle valve set and a connecting mechanism. The cam set is pivotally installed at the upper inlet end of the base, and a cam surface of the cam set abuts a top surface of the conical body of the variable venturi assembly. The throttle valve set is pivotally installed at the lower outlet end of the base, and the throttle valve set comprises a throttle valve for controlling the open/close of the lower outlet end. The connecting mechanism has one end connected to the cam set and the other connected to the throttle valve set.